Black-chinned Tilapia Sarotherodon Melanotheron Research Articles

Effects of seawater and freshwater challenges on the Gh/Igf system in the saline-tolerant blackchin tilapia (Sarotherodon melanotheron).

Prolactin (Prl) and growth hormone (Gh) as well as insulin-like growth factor 1 (Igf1) are involved in the physiological adaptation of fish to varying salinities. The Igfs have been also ascribed other physiological roles during development, growth, reproduction and immune regulation. However, the main emphasis in the investigation of osmoregulatory responses has been the endocrine, liver-derived Igf1 route and local regulation within the liver and osmoregulatory organs. Few studies have focused on the impact of salinity alterations on the Gh/Igf-system within the neuroendocrine and immune systems and particularly in a salinity-tolerant species, such as the blackchin tilapia Sarotherodon melanotheron. This species is tolerant to hypersalinity and saline variations, but it is confronted by severe climate changes in the Saloum inverse estuary. Here we investigated bidirectional effects of increased salinity followed by its decrease on the gene regulation of prl, gh, igf1, igf2, Gh receptor and the tumor-necrosis factor a. A mixed population of sexually mature 14-month old blackchin tilapia adapted to freshwater were first exposed to seawater for one week and then to fresh water for another week. Brain, pituitary, head kidney and spleen were excised at 4 h, 1, 2, 3 and 7 days after both exposures and revealed differential expression patterns. This investigation should give us a better understanding of the role of the Gh/Igf system within the neuroendocrine and immune organs and the impact of bidirectional saline challenges on fish osmoregulation in non-osmoregulatory organs, notably the complex orchestration of growth factors and cytokines.

Familiarity reduces aggression but does not modify acoustic communication in pairs of Nile tilapia (Oreochromis niloticus) and black-chinned tilapia (Sarotherodon melanotheron).

Reproduction involves multiple complex behaviours, and the effects of familiarity on such social interactions are seldom described in fish. This is particularly true for sound production and communication within aggressive or non-aggressive context. This study explores the effects of a common garden rearing without parental care of two closely related cichlid species (Nile tilapia Oreochromis niloticus and black-chinned tilapia Sarotherodon melanotheron) on their sound production features and social interactions. After 9months in common garden rearing, from embryonic stage to first maturity, sound production and associated behaviours were recorded on specimens of the two species in intraspecific and interspecific pairings. The authors found that fish were able to produce the same kind of sounds as those recorded in similar context for their parents. Drum sounds were associated to chasing, lateral attack and courtship in O. niloticus and only to fleeing or avoidance in S. melanotheron. Specific grunts were produced in chasing, after biting and in nest building by O. niloticus, and specific rolling sounds were associated to courtship in S. melanotheron. Sound production and behaviours were not correlated to sex steroid levels, but the number of sounds recorded in aggressive context was correlated to dominance in O. niloticus. The authors conclude that one generation of common garden rearing does not modify sound features, which remain specific and innate in the two cichlids. Despite the familiarity, O. niloticus remained dominant on S. melanotheron, but the aggressiveness between the two species decreased.

Population parameters, exploitation rate and diet of black-chinned Tilapia, Sarotherodon melanotheron Rüppell, 1852 (Pisces: Cichlidae), from Badagry Creek, Lagos, Nigeria

The black-chinned tilapia (Sarotherodon melanotheron) is a member of the cichlid family, which can be cultured to complement the output from a predominantly catfish aquaculture industry in Nigeria. In order to achieve this objective, it is important to study the bio-ecology of the fish to ascertain the exploitation status and the potential for culture. Fish were collected monthly from February to November 2018 from three sampling sites (Topo, Akarakumo and Ajido) in Badagry Creek, Lagos, Nigeria using gears like cast net, gill nets and traps. The samples were analysed for length-weight relationship, population parameters and feeding preference. The population dynamics of the stock was assessed by the Von Bertalanffy growth model (VBGM) using Electronic Length Frequency Analysis. The parameters of VBGM; asymptomatic length (L∞) and growth coefficient (K) were 20.46 cm and 0.62 year−1, respectively. The growth performance index (Ǿ) was 2.41 and the potential longevity (tmax) was 4.84 years. The total, natural and fishing mortalities were 1.06, 0.68 and 0.38 year−1, respectively. The exploitation rate was estimated as 0.36. The length at first maturity (L50) was 13.79 cm and the length at first capture (Lc) was 12.27 cm. E0.1, E0.5 and Emax are 0.60, 0.38 and 0.70, respectively. The dominant food items in the gut of the fish belong to the algae phylum, Chlorophyta. The study showed that S. melanotheron from Badagry Creek are planktivores and the exploitation rate of the fish is currently close to optimum and should be sustained at this level to prevent overexploitation.

Acoustic signals produced by Nile tilapia Oreochromis niloticus and black-chinned tilapia Sarotherodon melanotheron during intra- and interspecific pairings

We characterised, for the first-time, the sound production of black-chinned tilapia Sarotherodon melanotheron and show differences with that of Nile tilapia Oreochromis niloticus in a hybridization pairing context. Although both species were able to produce drum sounds, they showed different acoustic features. Drum sounds were produced in aggressive (chasing or lateral attack) and non-aggressive (courtship) contexts by O. niloticus but only in aggressive situations (fleeing or avoidance) by S. melanotheron. The second type of sounds produced by O. niloticus were grunts, produced in both aggressive (chasing and after biting) and non-aggressive contexts (nest building). The second type of sound produced by S. melanotheron was a rolling sound, produced only during courtship. Each species was able to produce common sounds (drum) and species-specific sounds (grunts and rolling). This implies that species can communicate without being able to understand each other because the sounds emitted may probably have different significance. Drumming corresponded only to aggressivity in S. melanotheron, whereas this was not true for O. niloticus. 11-ketotestosterone (11-kt) levels were significantly higher in male O. niloticus than male S. melanotheron, but there was no significant correlation between 11-kt or estradiol concentrations and the number of sounds produced in aggressive or non-aggressive behavioural contexts in either species. During interspecies interactions, O. niloticus drum sounds are likely considered to be aggressive by S. melanotheron and could potentially constitute a reproductive barrier between the two species.

Growth and mortality parameters of the black-chinned tilapia Sarotherodon melanotheron melanotheron (Pisces: Cichlidae) in a small lagoon in the Central Region of Ghana

This study quantified growth, mortality, and exploitation rate of the black-chinned tilapia (Sarotherodon melanotheron melanotheron) population in Etsir Lagoon, a small brackish waterbody at Abandze (5°11′ N, 1°5′ W) in the Central Region of Ghana for management of the stock. Fish samples were collected monthly between April 2014 and March 2015, and specimens measured 3.9–13.8 cm SL with a mode in the 7.0–7.9 cm length class. Analysis of the length-frequency data of 861 specimens using the ELEFAN method indicated a growth constant (K) of 0.93 yr−1, and asymptotic length (L∞) of 14.3 cm SL for the population. The short lifespan (tmax = 3.2 years) determined for the species and estimated growth parameters suggest stunting in the population, as in other brackish water populations in Ghana. The total mortality (Z), natural mortality (M), and fishing mortality (F) coefficients: 5.09 yr−1, 2.15 yr–1 and 2.95 yr−1, respectively, indicate fishing as a major contributor to total mortality. The calculated exploitation rate (E = 0.58) of the population suggests overexploitation of the stock, however, the all-year- round recruitment in the population probably ensures production at levels that compensate for its relatively high exploitation rate.

Reproductive behaviour of two tilapia species (Oreochromis niloticus, Linné, 1758; Sarotherodon melanotheron, Rüppel, 1852) in freshwater intra and interspecific pairing context

Nile tilapia Oreochromis niloticus (NT) and Black-chinned tilapia Sarotherodon melanotheron (BCT) are respectively characterized by fast growth and water salinity tolerance which attract the farmers who could take advantage of both species characteristics by producing hybrids reared in brackish or marine waters. Little information is however available about social interactions between the two species which are distinct by their mode of parental care (oral incubation). The objective of this study was to determine the behaviour of the two species, NT and BCT placed in freshwater intraspecific and interspecific pairing contexts. Females of both species (n=20 per species) were first isolated for 90days in a 60L aquarium to determine the average duration between spawning in the absence of males. With the approach of 4th spawning or after 90days of isolation, intra and interspecific pairing (fish average weight 200.4±5.1g) were made 10 times by pairing mode in a 350L aquarium. The day after fish pairing, 15min videos were recorded at one hour intervals from 8:00h to 17:00h, and courtship and aggressiveness behaviour were quantified. The results showed that isolated NT females had an average duration between two spawning of 15.9days. No spawning was observed in BCT females. Spawning events were observed in the NT intraspecific pairs, with strictly maternal oral egg incubations. Behavioural differences and some similarities were noted between the two species. NT male was the most dominant in front of females of both species and NT females showed dominance on BCT males. No clear hierarchy was observed in BCT pairs. Courtship behaviours were observed in all pairings with longer durations in NT pairs. Nest building was observed from 8:00h to 17:00h in both sexes of BCT and male NT. NT females built nests from 11:00h with longer durations when paired with males BCT than when paired with their conspecific males. These first results, reflecting behavioural plasticity in both species suggested that other breeding conditions favouring less aggressive behaviour could lead to a natural interspecific hybridization between NT and BCT.

Self-feeding behaviour and personality traits in tilapia: A comparative study between Oreochromis niloticus and Sarotherodon melanotheron

Hybridization aims at combining valuable traits from two species into a single group. Nile tilapia Oreochromis niloticus (NT) and Black-chinned tilapia Sarotherodon melanotheron (BCT) are respectively characterized by fast growth and water salinity tolerance which attract the breeders who could take advantage of both species. The first step is to characterize both species behavior in different contexts. The aim of this study was to compare the self-feeding behaviour between NT and BCT with a design allowing to reveal individual and group feed demand behaviour and then to identify the individual specialization that builds around the device and the food dispenser. The second objective was to estimate the links between the individual specialization and personality traits. To this aim, we recorded feed demand behaviour of both species using a computerized self-feeding device (two tanks for each species containing 20 PIT-tagged individuals with a male-female ratio of about 47%). Personality traits of all individuals were subsequently characterized with an open field test (OFT). The links between feed-demand and personality were then analyzed. Growth performances were not significantly different between NT and BCT but there was a strong tank effect. The individual specialization was similar in NT and BCT and similar to that previously observed in sea bass i.e. 1–3 individuals responsible for most of the feed demand activity in the tanks. Most NT individuals stayed in the shelter during the open field test while most of BCT individuals moved out of it. Overall, NT were shyer than BCT or the OFT was not adapted to NT. Linking the results of the self-feeding experiment and OFT in BCT, we found a strong positive correlation between the triggering activity and females’ shyness. Fish that spent more time inside than outside the shelter and which latency to emerge from shelter was longer, were characterized by a higher triggering activity (high-triggering fish). This study confirms the NT ability to use self-feeder devices and provides the first insight into the same ability in BCT and demonstrates links with personality traits. These results have a potential interest for the success of BCT and NT hybridization.

Assessment of chromium, nickel, cobalt and zinc in edible flesh of two tilapia fish species found in Bodo River, Rivers State, Nigeria

Oil exploration, exploitation, oil well fires and pipe-line vandalism are often reported to lead to high levels of pollution of the environment affecting water, land and air. As a result, the safety of specific fish species for human consumption is constantly in doubt and needs assessment. Guinean tilapia ( Tilapia guineensis ) and Blackchin tilapia ( Sarotherondon melanotheron ) are two of the highly consumed fish species in Bodo River. The level of chromium, nickel, cobalt and zinc in the flesh of Tilapia guineensis and Sarotherondon melanotheron found in Bodo River were studied using X-ray fluorescence (XRF). The amount of chromium found in the two fish species ranged between 10.3-10.5mg/kg, nickel 8.7-10.2mg/kg, cobalt 3.0-4mg/kg and zinc 71.2-74.5mg/kg. The levels of Cr, Ni, Co and Zn found in these two species of fish were compared to WHO maximum permissible levels of fish for consumption. The results showed that, fish from the study area contain amount of these metals investigated. This result will serve as a baseline for Food Agencies in Nigeria to certify safety of fishes from various rivers before they are sold for consumption to the public is hereby highlighted. Keywords: X-ray fluorescence, Chromium, nickel, cobalt, zinc, Guinean tilapia ( Tilapia guineensis ), Blackchin tilapia ( Sarotherodon melanotheron ), Bodo River

Common Garden Experiments Confirm the Impact of Salinity on Reproductive Traits that is Observed in Wild Populations of the Back-Chinned Tilapia Sarotherodon melanotheron

The black-chinned tilapia Sarotherodon melanotheron is a very hardy species, particularly notable for its ability to tolerate a wide range of environmental salinities. The impact of environmental salinity on reproductive traits has been well documented in this species under natural conditions, but few studies have been experimentally conducted to prove such a relationship. This study assessed the effects of different salinities on the reproductive traits of S. melanotheron in experimental conditions. The number of spawning eggs as well as the mean number and frequency of incubation showed significant relationships with ambient salinity. The average number of incubations and spawning eggs were lower in hypersaline water (70 psu) compared the freshwater (0 psu) and seawater (35 psu). However the egg quality, as measured by the percentage of black eggs, was higher in hypersaline water. These variations in reproductive traits do not reflect genetic differences among individuals because fish used in common garden experiments were obtained by natural breeding from couples, the initial brood stock of which was from the same wild population. The results therefore confirm findings of previous studies in natural habitats, where variations in salinity are associated with differences in reproductive traits among populations. The lower number and frequent incubations recorded in hypersaline water could be an adaptive response to sustain the population dynamics despite the constraints imposed by extreme salinity.

Effects of hydrographic conditions of ponds on juvenile fish assemblages in the Kakum mangrove system, Ghana

The importance of mangrove ecosystems as nursery grounds for fishes is well established and documented. This paper reports on the possible role of hydrographic dynamics in the selection and utilization of tropical mangrove ponds as nursery habitats for juvenile fishes of ecological and commercial importance. The study was conducted in the Kakum River Estuary mangrove ecosystem near Elmina in the Central Region of Ghana during the peak of the monsoon season. Fish assemblages were sampled using a cast net and a pole seine. Aspects of hydrographic conditions of the ponds were studied. A total of 265 fish specimens, belonging to 18 species and 12 families were sampled. The commonest fish was the blackchinned tilapia Sarotherodon melanotheron, a typical brackish water fish in West Africa, which accounted for 66.4% of the total fish sampled. Ten of the 18 species belonging to 7 families, namely Elops lacerta, Eucinostomus melanopterus, Porogobius schlegelii, Gobionellus occidentalis, Mugil bananensis, Liza falcipinnis, Epinephelus sp., Serranus accraensis, Penaeus notialis and Callinectes amnicola were of marine origin. Spatial and temporal variations in the prevailing hydrographic conditions appeared to influence the fish species composition, density and size classes to varying degrees. Changes in salinity, dissolved oxygen, pH, conductivity and pond size correlated significantly with abundance of juvenile fish. Major fluctuations in fish species composition occurred on a weekly basis with changing pond depth and volume, indicating the dynamic nature of mangroves ponds that may serve the ecological needs of different species over time. Smaller juvenile fishes seemed better adapted to high variations in hydrographic conditions compared to larger juveniles. Higher fish densities and lower species diversity were encountered when the ponds were shallow compared to deep ponds. The utilization of mangrove tidal ponds as nurseries by juvenile fish may therefore be influenced primarily by the salinity and pond size.

First report on the occurrence of invasive black-chin tilapia Sarotherodon melanotheron (Ruppell, 1852) in Manila Bay and of Mayan cichlid Cichlasoma urophthalmus (Gunther, 1892) in the Philippines

We report the presence of blackchin tilapia, Sarotherodon melanotheron, in the coastal waters of Manila Bay and in the river tributary of Hagonoy, Bulacan, suggesting its possible range expansion. The occurrence of the native Central American Mayan cichlid, Cichlosoma urophthalmus, is also putatively confirmed for the first time in Hagonoy, Bulacan. While morphological features, morphometric characters, and meristic counts of the current populations match those reported elsewhere for these species, further genetic work is required to confirm their identification and possibly provide information on their source. Negative impacts of the existence of the two species due to competitive interactions have already been anecdotally reported, however, no empirical scientific evidence is available to provide verification. Therefore, studies on the potential ecological impacts should be done, especially because the two species were already reported as notoriously invasive.

Plasticity of gene expression according to salinity in the testis of broodstock and F1 black-chinned tilapia, Sarotherodon melanotheron heudelotii.

The black-chinned tilapia Sarotherodon melanotheron heudelotii Rüppell 1852 (Teleostei, Cichlidae) displays remarkable acclimation capacities. When exposed to drastic changes of salinity, which can be the case in its natural habitat, it develops quick physiological responses and keeps reproducing. The present study focused on the physiological impact of salinity on male reproductive capacities, using gene expression as a proxy of acclimation process. Two series of experimental fish were investigated: the first one was composed of fish maintained in freshwater for several generations and newly acclimated to salinities of 35 and 70, whereas the second one consisted of the descendants of the latter born and were raised under their native salinity. Expression patterns of 43 candidate genes previously identified from the testes of wild males was investigated in the three salinities and two generations. Twenty of them showed significant expression differences between salinities, and their predicted function revealed that most of them are involved in the osmotic tolerance of sperm cells and/or in the maintenance of sperm motility. A high level of expression variation was evidenced, especially for fish maintained in freshwater. In spite of this, gene expression patterns allowed the differentiation between fish raised in freshwater and those maintained in hypersaline water in both generations. Altogether, the results presented here suggest that this high variability of expression is likely to ensure the reproductive success of this species under varying salinities.

Egg production in the euryhaline tilapia,Sarotherodon melanotheron heudelotii, experimentally maintained in fresh, sea and hypersaline waters

Through the experiments presented here we wanted to test whether egg production of the black-chinned tilapia Sarotherodon melanotheron heudelotii under experimental conditions varies as a function of ambient salinity (fresh waters vs. sea waters vs. hypersaline waters, 0, 35 and 70, respectively) and whether these responses differ between fish acclimated within a few weeks from fresh water to saline and hypersaline environments (experiments E1 and E2, monitoring over 10 and 18 weeks), and individuals born and raised all life long at the experimental salinities (E3, monitoring over 18 weeks). In total, 233 spawns were collected. In each of the three experiments, the reproductive investment (gram of egg per gram of female over 2 weeks) did not differ between salinities of 0 and 35, whereas it was 2–3 times lower at 70 than at 0–35, because of lower spawning frequency (E1-E3), smaller clutch size (E1) and lower spawn mass (E1-E3). Finally, fish acclimated to salinity from fresh water over a few weeks and those maintained at a particular salinity all life long showed similar reproductive traits, thereby emphasizing the remarkable physiological plasticity of this species.

Analysis of the black-chinned tilapiaSarotherodon melanotheron heudelotiireproducing under a wide range of salinities: from RNA-seq to candidate genes

The black-chinned tilapia Sarotherodon melanotheron heudelotii is an ecologically appealing model as it shows exceptional adaptive capacities, especially with regard to salinity. In spite of this, this species is devoid of genomic resources, which impedes the understanding of such remarkable features. De novo assembly of transcript sequences produced by next-generation sequencing technologies offers a rapid approach to obtain expressed gene sequences for non-model organisms. It also facilitates the development of quantitative real-time PCR (qPCR) assays for analysing gene expression under different environmental conditions. Nevertheless, obtaining accurate and reliable qPCR results from such data requires a number of validations prior to interpretation. The transcriptome of S.melanotheron was sequenced to discover transcripts potentially involved in the plasticity of male reproduction in response to salinity variations. A set of 54 candidate and reference genes was selected through a digital gene expression (DGE) approach, and a de novo qPCR assay using these genes was validated for further detailed expression analyses. A user-friendly web interface was created for easy handling of the sequence data. This sequence collection represents a major transcriptomic resource for S.melanotheron and will provide a useful tool for functional genomics and genetics studies.

The impact of environmental degradation on reproduction of the black-chinned tilapia Sarotherodon melanotheron from various coastal marine, estuarine and freshwater habitats

There is growing evidence that climate change has greatly altered environmental conditions in many aquatic ecosystems over the last decades, leading to changes in fish distribution and life history traits. Recent works conducted in Senegalese and Gambian coastal marine, estuarine and freshwater ecosystems have shown important changes in the intensity, frequency and breeding timing of wild population of Sarotherodon melanotheron in response to changes in salinity regimes. In addition to salinity, this study investigates the potential influences of other environmental factors that have received less attention on the reproduction of S. melanotheron from three different aquatic ecosystems in Senegal. The results demonstrate that day-length and temperature affect sexual maturity in both males and females from Guiers Lake and Hann Bay, but no such effects were found in upstream of the Saloum Estuary, where the spawning activity seems to be under the synergetic control of rainfall and salinity that apparently predominate over all the other ambient factors. This study demonstrated for the first time that aside from photoperiod and temperature, rainfall also influences fish reproduction in Hann Bay probably through its effects on water quality. Furthermore, our results confirm previous findings that changes in salinity regimes resulting from seasonal variations in precipitation and evaporation are the ultimate causes of temporal changes in the reproductive activity of the species in this estuary.

Osmoregulatory strategies in natural populations of the black-chinned tilapia Sarotherodon melanotheron exposed to extreme salinities in West African estuaries

The effect of salinity was studied in natural populations of the black-chinned tilapia (Sarotherodon melanotheron) from West Africa. This euryhaline species colonizes nearly all coastal environments from bays to lagoons characterized by salinities ranging from fresh water to hypersaline water over 100 ‰. Individuals were sampled during the dry season at several locations characterized by different levels of salinity (3-102 ‰). Their osmotic status and their gills were analyzed. The branchial mitochondria-rich cells (MRC), localized at the basis of the filaments and along the lamellae in fish taken from the saline stations, showed a wide plasticity with significant differences in their number and size. The most striking results were a significant larger area (≈3x) and a higher number (≈55x) of MRC at high salinity (102 ‰) compared to low salinity (3 ‰). The major ion transporters and channels were localized by immunocytochemistry and different expression patterns have been recorded between stations. Despite an increased Na⁺/K⁺-ATPase (NKA) α-subunit expression and NKA activity, pointing to an increased monovalent ion excretion, a severe osmotic imbalance was recorded in animals living in hypersaline environments.

Variation in gene expression along a salinity gradient in wild populations of the euryhaline black‐chinned tilapia Sarotherodon melanotheron

This study evaluated variation in expression of 11 genes within and among six wild populations of the black-chinned tilapia Sarotherodon melanotheron distributed along a salinity gradient from 0 to 100. Previous laboratory studies had shown that expression of these genes was sensitive to water salinity; the current study confirmed that a number of them also varied in expression in wild populations along the salinity gradient. Principal component analysis (PCA) first distinguished two, not mutually exclusive, sets of genes: trade-off genes that were highly expressed at one or other extreme of the salinity gradient and stress genes that were up-regulated at the two salinity extremes (i.e. a U-shaped expression pattern). The PCA clearly partitioned the populations into three groups based on their gene expression patterns and their position along the salinity gradient: a freshwater (GL; 0) population, four brackish and seawater (GB, HB, SM, SF; ranging from 20 to 50) populations and a hypersaline (SK, 100) population. Individual variation in gene expression was significantly greater within the populations at the extreme compared to intermediate salinities. These results reveal phenotypically plastic regulation of gene expression in S. melanotheron, and greater osmoregulatory and plasticity costs at extreme salinities, where fitness-related traits are known to be altered.

Seasonal Accumulations of Some Heavy Metal in Water, Sediment and Tissues of Black-Chinned Tilapia Sarotherodon melanotheron from Biétri Bay in Ebrié Lagoon, Ivory Coast

The seasonal accumulation of cadmium, copper, lead, mercury and zinc was determined in sediments, water, and black-chinned tilapia (Sarotherodon melanotheron; muscle, brain, kidney and liver tissues) collected monthly from Biétri Bay. The mean water concentration of metals (in mgL(-1)) ranged from 0.01 to 0.30 (mercury), 0.02-0.26 (cadmium), 2.40-4.80 (lead), 9.05-9.68 (copper), and 12.05-19.87 (zinc). The seasonal variations showed a significant difference in the levels of mercury, cadmium and lead among season. The highest mercury (0.30±0.02μgL(-1)), cadmium (0.26±0.02mgL(-1)) and lead (4.80±1.03mgL(-1)) levels were observed during dry season, while the lowest levels (0.21±0.01, 0.02±0.01 and 2.40±0.02mgL(-1), respectively mercury, cadmium and lead) were measured during rainy season. The average cadmium (0.58±0.36mgL(-1)), copper (42.15±19.40mgL(-1)), lead (58.47±38.10mgkg(-1)), mercury (0.79±0.47 μgkg(-1)) and zinc (187.58±76.99mgkg(-1)) concentrations determined in Biétri Bay sediments showed a similar trend as in water. The seasonal variations of mercury, cadmium and lead in tissues revealed that these metals were higher concentrated during dry and swelling seasons. The levels of zinc and copper followed by lead were higher in the tissues. The order of tissues metals concentrations was: kidney > liver > brain > muscle.

Comparative Analysis of Reproductive Traits in Black-Chinned Tilapia Females from Various Coastal Marine, Estuarine and Freshwater Ecosystems

The black-chinned tilapia Sarotherodon melanotheron is a marine teleost characterised by an extreme euryhalinity. However, beyond a certain threshold at very high salinity, the species exhibits impaired growth and precocious reproduction. In this study, the relationships between reproductive parameters, environmental salinity and condition factor were investigated in wild populations of this species that were sampled in two consecutive years (2003 and 2004) from three locations in Senegal with different salinities: Guiers lake (freshwater, 0 psu), Hann bay (seawater, 37 psu) and Saloum estuary (hypersaline water, 66–127 psu). The highest absolute fecundity and spawning weight were recorded in seawater by comparison to either freshwater or hypersaline water whereas the poorest condition factors were observed in the most saline sampling site. These results reflect higher resource allocation to the reproduction due to the lowest costs of adaptation to salinity in seawater (the natural environment of this species) rather than differences in food resources at sites and/or efficiency at foraging and prey availability. Fecundities, oocyte size as well as spawning weight were consistent from year to year. However, the relative fecundity in the Saloum estuary varied significantly between the dry and rainy raisons with higher values in the wet season, which seems to reflect seasonal variations in environmental salinity. Such a reproductive tactic of producing large amounts of eggs in the rainy season when the salinity in the estuary was lower, would give the fry a better chance at survival and therefore assures a high larval recruitment. An inverse correlation was found between relative fecundity and oocyte size at the two extreme salinity locations, indicating that S. melanotheron has different reproductive strategies in these ecosystems. The adaptive significance of these two reproductive modes is discussed in regard to the heavy osmotic constraint imposed by extreme salinities and high inter-specific competition.

Pen Culture of the Black-Chinned Tilapia, <i>Sarotherodon Melanotheron</i> in the Aglor Lagoon in Ghana

Pen-fish-culture as a culture-based fisheries approach was investigated in the Aglor Lagoon from December 2003 to June, 2004. The fish used in the study was the Black-chinned tilapia Sarotherodon melanotheron. The growth performance of S. melanotheron cultured for six months in the Aglor Lagoon under three different treatments were monitored. In the first treatment, the cultured fish was fed with a feed of 29.80 % protein at 3 % body weight once a day. In the second treatment, bamboo was stacked at a density of 6 per metre square in pens to serve as substrate for periphyton growth and development. In the third treatment, there was no feeding (control). There was significant difference in growth between the fed and the unfed S. melanotheron in the pens, with no significant difference in growth between the fish that subsisted on periphyton de-veloped on bamboo and the other treatments. S. melanotheron cultured in the bamboo equipped pens had the best condition factor of 3.57 ± 0.23. The experimental values of b obtained from the length-weight relationship (W = aLb) for the three treatments were 2.07, 2.13 and 2.80 for feeding, unfed and bamboo respectively. From the results, the least yield was obtained from the unfed control pen (0.045 kg/m2), whilst the highest was from the bamboo equipped pens (0.183 kg/m2).